The present invention relates to a magnet movable electromagnetic actuator for moving and positioning an object with satisfactory responsivity.
Conventionally, an electromagnetic solenoid (actuator) in which voltage is applied to an exciting coil to apply a linear motion to a movable core by a magnetic force is well known as a reciprocation apparatus for magnetically moving an object. Although a structure of this electromagnetic solenoid is simple, the electromagnetic solenoid includes a core inside the coil. Therefore, it is difficult to improve electrical responsivity. Moreover, because thrust cannot be generated when a current is not passed, uses of the electromagnetic solenoid are limited.
To cope with these problems, large voltage is applied on startup or positioning in non-energization is carried out by using a spring. Therefore, complication of the structure and increase in the number of parts are inevitable.
It is an object of the present invention to provide a magnet movable electromagnetic actuator for generating steady-state thrust in a short time with satisfactory responsivity without applying large voltage on startup unlike the prior-art electromagnetic solenoid.
It is another object of the invention to provide a magnet movable electromagnetic actuator in which a movable member can be easily retained in non-energization.
It is yet another object of the invention to provide a small-sized and inexpensive magnet movable electromagnetic actuator including the small number of parts, the electromagnetic actuator showing the above-described features by a simple structure in which a cylindrical permanent magnet polarized in a radial direction is used.
To achieve the above object, a first electromagnetic actuator of the invention comprises: an annular exciting coil; a main yoke surrounding a periphery of the exciting coil and having at a portion of the main yoke a pair of polar teeth positioned to face each other at axial opposite end portions of a central hole of the exciting coil; and a cylindrical permanent magnet disposed in the central hole of the exciting coil to be movable in an axial direction of the central hole and polarized into a north pole and a south pole in a radial direction.
A second magnet movable electromagnetic actuator of the invention comprises: an annular exciting coil; a main yoke surrounding a periphery of the exciting coil and having at a portion of the main yoke a pair of polar teeth positioned to face each other at axial opposite end portions of an outer periphery of the exciting coil; and a cylindrical permanent magnet disposed on an outer peripheral side of the exciting coil to be movable in an axial direction of the coil and polarized into a north pole and a south pole in a radial direction.
In the first and second magnetic movable electromagnetic actuators having the above structures, if the exciting coil is energized, the one polar tooth of the main yoke becomes the north pole while the other polar tooth becomes the south pole according to a direction of the current. If the magnetic poles generated in these polar teeth and a magnetic pole of the permanent magnet on a side facing the polar teeth are different from each other, an attracting force acts between them. If they are the same as each other, repulsion acts between them. Therefore, these forces become axial thrust acting on the permanent magnet and the permanent magnet moves in the axial direction in the central hole of the coil or outside the coil. If the exciting coil is energized in a reverse direction, the magnetic poles, i.e., the north pole and the south pole generated in both the polar teeth of the main yoke are reverse to the above-described case. As a result, the thrust acting on the permanent magnet is also in a reversed direction and the permanent magnet moves in a reverse direction.
As described above, according to the invention, it is advantageously possible to generate steady-state thrust in a short time with satisfactory responsivity without applying large voltage on startup unlike the prior-art electromagnetic solenoid.
In the invention, a cylindrical back yoke positioned coaxially with the cylindrical permanent magnet may be provided on an opposite side to the exciting coil through the permanent magnet, i.e., inside the permanent magnet in the first electromagnetic actuator and outside the permanent magnet in the second electromagnetic actuator. With this structure, because a magnetic path extending from the one polar tooth through the permanent magnet and the back yoke to reach the other polar tooth can be formed, it is possible to reduce a magnetic reluctance and to further increase thrust and the magnetic adsorbing force of the permanent magnet.
If the back yoke is formed to have such a thickness as to be magnetically saturated by a magnetomotive force of the permanent magnet, the permanent magnet can be retained in a neutral position by a magnetic force when the exciting coil is not energized. If the back yoke is formed to have such a thickness as not to be magnetically saturated by a magnetomotive force of the permanent magnet, the permanent magnet can be retained in two positions, i.e., a forward movement end or a rearward movement end by a magnetic force when the exciting coil is not energized.
According to the invention, as a third electromagnetic actuator, there is provided a magnet movable electromagnetic actuator comprising: an annular exciting coil; an annular main yoke surrounding a periphery of the exciting coil and having at a portion of the main yoke a pair of polar teeth positioned to face each other at axial opposite end portions of a central hole of the exciting coil; a cover and a cap respectively mounted to axial opposite end portions of the main yoke to form a casing with the main yoke; a magnet chamber formed inside the casing and having an outer periphery surrounded by the exciting coil and the pair of polar teeth; a permanent magnet formed in a cylindrical shape, polarized into a north pole and a south pole in a radial direction, and disposed in the magnet chamber inside the exciting coil and the polar teeth to be movable in an axial direction of the casing; a magnet holder for holding the per manent magnet and movable with the permanent magnet; and an output shaft passing through a central portion of the magnet chamber to slide in the axial direction of the casing and connected to the magnet holder.
The cylindrical back yoke may be mounted in a fixed manner to the casing to be positioned concentrically with the permanent magnet inside the permanent magnet.
The magnet holder may be repulsed by a spring in a returning direction.